1. Field of the Invention
The present invention relates to a data transmission method, a data transmission apparatus, a data recording medium, a data reception method, a data transmission apparatus, a data transmission/reception method, and a data transmission/reception apparatus which can preferably be used when transmitting an electronic mail.
2. Description of the Prior Art
With increase of communication through a network such as the Internet, there has arisen a problem of security in a network communication.
For example, in a communication processing service handling a personal information such as a mail box, a security technique is remarkably important in order to prevent information from being stolen or destroyed by other persons. There are two types of security techniques. One of them is a security technique using a password system in which a password is assigned to an information accumulated so that the information cannot be fetched by other persons. The other is a security technique using an encryption system in which meaning of the information cannot be understood without a key to decipher the information.
When transmitting a data through the Internet in which a data transmission route is unspecified, the encryption is used in most of cases, assuming that the data is wire-tapped by other persons.
It should be noted that the electronic mail can easily be broadcasted or transferred, and it is often the case that a user creates a new message citing a data or a text from another person. When such a message is transmitted, the data enciphered can easily be deciphered using the citation as a clue.
For example, if a wire-tapper A can fetch a part of a pair of a plain message M and a cipher text C created by a person to be wire-tapped, the wire-tapper A can decipher the enciphering method according to the plain message M and the cipher text C without using any decoding key.
Here, it is assumed that the wire tapper A transmits a message as an electronic mail to the person B to be wire-tapped. As shown in FIG. 1, the person a creates another message citing A""s message (step S1) and enciphers the message in a encryption circuit 31 so as to be transmitted as an electronic mail to a third person D. In this case, it is assumed that only the person D can read the message which has been decoded by a decoding circuit 32 (step S3). However, if the person A can wire-tap the cipher text C transmitted from B to D (step S2), then the person A can get a part of a pair of the plain message M and the cipher text C, which enables person A to decipher without using a decoding key.
There have been two types of deciphering or code breaking often used: use of an identifier such as xe2x80x9c greater than xe2x80x9d often used when citing another message or a stereotype message such as xe2x80x9cDear sirsxe2x80x9d as clue to decipherment (known-plain text attack); and transmitting a simple message to a person to be wire-tapped so that a cipher text of the simple message is wire-tapped for use in deciphering (chosen-plain text attack).
It is therefore an object of the present invention to provide a data transmission method, a data transmission apparatus, a data recording medium, a data reception method, a data reception apparatus, a data transmission/reception method, and a data transmission/reception apparatus which can prevent decipherment of a most important message and data even if a plain message or an enciphered message is wire-tapped
In order to achieve the aforementioned object, the data transmission method according to the present invention comprises: a step of assigning an identifier to a particular data; a step of executing different encryption processes to a data having the identifier and a data not having the identifier; and a step of transmitting data which have been enciphered.
The data transmission apparatus according to the present invention comprises: identifier assigning means for assigning an identifier to a particular data; encryption means for executing different encryption processes to a data having the identifier and a data not having the identifier; and transmission means for transmitting data which have been enciphered.
The program recording/transfer medium according to the present invention contains or transfers a computer program for assigning an identifier for a particular data, executing different encryption processes to a data having the identifier and a data not having the identifier, and transmitting an enciphered data.
The data reception method according to the present invention comprises a step of receiving a data and executing different decoding processes to a data having an identifier and a data not having the identifier.
The data reception apparatus according to the present invention comprises: reception means for receiving an enciphered data; and decoding means for executing different decoding processes to a data having an identifier and a data not having the identifier.
The program recording/transfer medium according to the present invention contains or transfers a computer program for executing different decoding processes for a data received and containing an identifier and a data received and not containing the identifier.
The data transmission/reception method according to the present invention comprises: a step of assigning an identifier to a particular data; a step of executing different encryption processes to a data having the identifier and a data not having the identifier; a step of transmitting a data which has been subjected to encryption; a step of receiving the data; and a step for executing different decoding processes to a data having the identifier and a data not having the identifier.
The data transmission/reception apparatus according to the present invention comprises:
a data transmission block including: identifier assigning means for assigning an identifier to a particular data; enciphering means for executing different encryption processes to a data having the identifier and a data not having the identifier; and transmission means for transmitting a data which has been subjected to encryption; and
a data reception block including: reception means for receiving the data; and decoding means for executing different decoding processes to a data having the identifier and a data not having the identifier.
The program recording/transfer medium according to the present invention contains or transfers:
a first computer program for assigning an identifier to a particular data, executing different encryption processes to a data having the identifier and a data not having the identifier, and transmitting a data which has been enciphered; and
a second computer program for executing different decoding processes to a data received and having the identifier and a data received and not having the identifier.